This invention relates to data communication systems employing wireless subsystems and more particularly to arrangements for indicating enhanced capabilities of such subsystems to wireless handsets seeking access to those capabilities via such subsystems.
In order for wireless handsets to establish a transmission path to a desired destination through a data communication system having a wireless subsystem(s), it is necessary for the wireless facilities to exchange signaling information with the handset. In the usual case where the subsystem has a base station equipped to operate in a first mode employing voice or low speed data communications (“first mode”), specific first mode signaling is used to establish the connection when the wireless handset also operates in such first mode.
Dual mode wireless handsets are now available that can selectively operate either in such first mode or in a second mode that can support an enhanced capability such as transmitting and receiving high speed data messages over a wireless subsystem that has corresponding high-speed capability. This is advantageous, for example, where a dual mode handset that is initially connected in the first mode with a low-speed first base station at one cellsite is handed off to a second base station that is disposed at a second cellsite and that is collocated with a third base station capable of transmitting high speed data in the second mode. In such case, the handset can be switched into the second mode in response to signals indicative of the enhanced capability of the third base station. However, upgrading an existing base station by adding facilities to provide such enhanced signaling to a dual-mode handset can add significantly to the costs of setting up and operating the associated wireless subsystem.